The present invention relates to disk drive control circuits, and more specifically to a CMOS disk drive control having back-EMF blocking circuitry.
During the power down operation of a disk drive, it is desirable to move the recording or pick up head off the storage medium to minimize damage to the head and the medium, and to minimize friction between the head and the medium when power is reapplied to the disk drive.
Since power is not available from the main power supply, an alternate power source must be made available to retract the head. A typical alternate power source is provided by the back electromotive force (back-EMF) of the spindle motor. Typically, a blocking diode prevents power from the spindle motor from being dissipated through the main power supply circuitry. Unfortunately, these diodes have been bipolar and discrete devices, which become less attractive for use in disk drive control circuits as disk drive form factors shrink.
Therefore, it would be desirable to combine a blocking diode with other disk drive control circuitry on a standard CMOS integrated circuit chip.